The present invention relates to a cathode ray tube, and more particularly to an improvement in the panel of a cathode ray tube.
Generally, a cathode ray tube has such elements as a neck, a funnel, and a panel. In such a cathode ray tube, an assembled electron gun is installed in a predetermined position in the neck, and a phosphor screen is formed on the inner surface of the panel. A shadow mask is installed inside the cathode ray tube and spaced apart from the phosphor screen at a predetermined distance. In a cathode ray tube constructed as above, the inside pressure of the tube is at a high vacuum, approximately 10.sup.-6 to 10.sup.-7 mmHg, so as to easily emit an electron beam and allow it to proceed away from the electron gun.
By forming the tube in a high vacuum state, the exterior of the tube is under great atmospheric pressure. Accordingly, as illustrated in FIG. 1, due to the structural characteristic of the circumference of the tube, a location 1b on the funnel as well as a location la on the panel are subjected to compressive stress. A periphery location 1c on the funnel and panel is subjected to tensile stress, which weakens the structural aspects of location 1c. Therefore, when a highly evacuated cathode ray tube implodes, there is dangerous flying glass at its periphery. Hence, a safe tube should be manufactured by reinforcing the structurally weak portions. For this purpose, a tension band is conventionally employed to reinforce the periphery of the funnel and panel. Also, the periphery of the panel is made to be relatively thicker than the center of the panel.
However, since the panel of a cathode ray tube is substantially rectangular in shape and due to the structural characteristics of a cathode ray tube, the deforming force caused by atmospheric pressure becomes greatest along the edges of the shorter axis of the panel, the least along its diagonal, and the mean along its longer axis. Based upon consideration of the above-described matters, the panel is formed to vary in thickness. That is, the panel is the thinnest along the diagonal line of the panel, and is the thickest along the edges of the shorter axis.
Therefore, contour lines 2 drawn along the same thickness, as illustrated in FIG. 2, of a panel 1 constructed as above, have discontinuous points at periphery 3 of a screen. As a result, a problem occurs wherein the picture is distorted at the screen's periphery due to the discontinuity of contour lines 2 at periphery 3.